I've mentioned previously that I have this filter and its problem of floating out from the corner of the tank, and which I've rectified with magnets. For anyone else who finds themself in this situation, the following is how I addressed it:
(1) The first ‘mistake’ (but NB see later) I did was to buy one of these
https://www.jbl.de/en/products/detail/4654/jbl-cp-i-magnetic-holder, thinking it would solve the problem if I stuck it on the outside of the tank. However, there was no magnet part on the filter itself, so I contacted JBL to ask about this – it transpired that this was made for an earlier, non-Greenline, model of the filter than the one I had. [However, see (3).]
(2) Instead, I bought one of these
https://www.petsathome.com/shop/en/pets/zoo-med-magclip-magnetic-suction-cups-(online-only) but these are not strong enough in their own right, despite being advertised as industrial strength. [However, see (4).]
(3) Next, I contacted several companies and First4Magnets.com Customer Care Team (Juan was my very helpful adviser) contacted their engineers, etc, who suggested this
https://www.first4magnets.com/circular-disc-rod-c34/21-5mm-dia-x-11-4mm-thick-rubber-coated-n42-neodymium-magnet-9-9kg-pull-p11183#ps_1-10642 or this
https://www.first4magnets.com/circular-disc-rod-c34/21-5mm-dia-x-11-4mm-thick-rubber-coated-n42-neodymium-magnet-9-9kg-pull-p11183#ps_1-10642 . I ordered one of each. These were based on the weight of the CristalProfi i80 filter of 2 baskets weighing 499g and my aquarium glass thickness being 5mm. Both are equally good and sit inside the lower of the 2 filter baskets (one on each ‘side’) and attach to the JBL magnetic holder on the outside of the tank.
(4) In the upper of the 2 filter baskets, I use the ZooMed mag-clip flat part, with the corresponding ‘lid’ part on the outside of the glass. This is for added security but it’s not particularly strong and certainly wouldn’t be sufficient in its own right.
(5) With the magnets in the lower baskets pulling the filter in snugly against the glass, the uppermost part of the filter (containing the impeller and outflow pipe) sits comparatively less snugly against the glass – in part due to the presence of the suction cups. As some of my inhabitants had a tendency to squeeze themselves behind the filter, I slide filter wool/sponge in the side of this uppermost section using aquascaping tweezers – a bit of a faff every fortnightly filter maintenance, as is the removal and re-positioning of the magnets and attempts not to injure myself in the process as they certainly are of industrial strength!